There are numerous inherited human metabolic disorders, most of which are recessive. Many have devastating effects that may include a combination of several clinical features, such as severe mental retardation, impairment of the peripheral nervous system, blindness, hearing deficiency and organomegaly. Most of the disorders are rare. However, the majority of such disorders cannot be treated by drugs.
Galactokinase deficiency is one of three known forms of galactosemia. The other forms are galactose-1-phosphate uridyltransferase deficiency and UDP-galactose-4-epimerase deficiency. All three enzymes are involved in galactose metabolism, i.e., the conversion of galactose to glucose in the body. Galactokinase deficiency is inherited as an autosomal recessive trait with a heterozygote frequency estimated to be 0.2% in the general population (see, e.g., Levy et al., J. Pediatr., 92:871-877 (1978)). Patients with homozygous galactokinase deficiency usually become symptomatic in the early infantile period showing galactosemia, galactosura, increased galactitol levels, cataracts and in a few cases, mental retardation (Segal et al., J. Pediatr., 95:750-752 (1979)). These symptoms usually improve dramatically with the administration of a galactose free diet. Heterozygotes for galactokinase deficiency are prone to presenile cataracts with the onset during 20-50 years of age (Stambolian et al., Invest. Ophthal. Vis. Sci., 27:429-433 (1986)).
Galactokinase activity has been found in a variety of mammalian tissues, including liver, kidney, brain, lens, placenta, erythrocytes and leukocytes. While the protein has been purified from E. coli, the purification of the protein from mammalian tissues has proven difficult due to its low cellular concentration. In addition, the molecular basis of galactokinase deficiency is unknown.
This invention provides a human galactokinase gene. The DNAs of this invention, such as the specific sequences disclosed herein, are useful in that they encode the genetic information required for expression of this protein. Additionally, the sequences may be used as probes in order to isolate and identify additional members, of the family, type and/or subtype as well mutations which may form the basis of galactokinase deficiency which may be characterized by site-specific mutations or by atypical expression of the galactokinase gene. The galactokinase gene is also useful as a diagnostic agent to identify mutant galactokinase proteins or as a therapeutic agent via gene therapy.
The first clinical trials of gene therapy began in 1990. Since that time, more than 70 clinical trial protocols have been reviewed and approved by a regulatory authority such as the NIH's Recombinant Advisory Committee (RAC), see, e.g., Anderson, W. F., Human Gene Therapy, 5:281-282 (1994). The therapeutic treatment of diseases and disorders by gene therapy involves the transfer and stable insertion of new genetic information into cells. The correction of a genetic defect by re-introduction of the normal allele of a gene has hence demonstrated that this concept is clinically feasible (see, e.g., Rosenberg et al., New Eng. J. Med., 323: 570 (1990)).
These and additional uses for the reagents described herein will become apparent to those of ordinary skill in the art upon reading this specification.